1. Field of the Invention
The invention relates to the field of machine tools and more particularly to devices for holding workpieces in place during machining operations.
2. Description of the Related Art
Many machining operations require a workpiece to be held in a stationary position. Various types of clamps and vises are used for this purpose. Prior clamping devices used laterally-applied forces to hold the workpiece in place so that, when the force of a machining tool (e.g., a cutting edge or polishing surface) is applied to the workpiece, the workpiece does not move, as the machining tool force is counteracted by an opposite stabilizing force applied by the clamping device. This holds the piece in place; however, when the machining operation is finished and the force of the tool surface is removed from the workpiece, the workpiece can jump or pop out of the clamp. This has been overcome in the prior art with devices having a gripping member which engages the workpiece vertically as well, and thereby providing a force to stabilize the workpiece when the cutting surface is removed.
An example of such a device is described in U.S. Pat. No. 5,624,106 (“'106 Patent”), filed Nov. 13, 1995, and issued as a United States patent on Apr. 29, 1997, the entire disclosure of which is incorporated herein by reference. FIG. 1 depicts a prior art gripping device A according to the '106 Patent for holding a workpiece in position. The depicted gripping device A includes a fixture 2 having a working surface 4 and at least one hole 6; a stop 8 rising above working surface 4 of fixture 2; a fastener 10 and a gripping member 12. Gripping member 12 has a through bore 14 for receiving fastener 10 and a gripper wall 16 adapted to engage the workpiece. When fastener 10 is secured to hole 6 of fixture 2, either by being received in a threaded hole 6 or a threaded nut (not shown) on the reverse side of fixture 2, gripping member 12 slides toward stop 8 and gripper wall 16 applies a downward inward holding force on the workpiece. This holding force begins where the workpiece abuts gripper wall 16 and arcs downward through the workpiece to working surface 4 of fixture 2, thereby pushing the workpiece in towards stop 8 and down against working surface 4. The downward inward holding force can be created by a draft angle formed on gripper wall 16, or through other techniques described in the '106 Patent.
However, using such a device requires that the fastener be inserted into the fixture at an appropriate distance from the workpiece such that the gripper wall will engage the stock (or workpiece) when the fastener is secured to the fixture. The terms “stock” and “workpiece” are used herein interchangeably to refer to the material(s) held in place by the device. Failure to engage the stock in this manner may require resetting the machining operation, resulting in lost time and efficiency.